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Effects of different molecular weight fractions of natural organic matter on the adsorption and desorption of cadmium in purple soil
Received:December 12, 2018  
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KeyWord:natural organic matter;molecular weight;soil;Cd;adsorption-desorption
Author NameAffiliationE-mail
YE Bi-ying College of Resources and Environment, Southwest University, Chongqing 400716, China
Chongqing Key Laboratory of Agricultural Resources and Environment, Chongqing 400716, China
China Key Laboratory of the Three Gorges Reservoir Region's Eco-Environment, Ministry of Education, Chongqing 400716, China 
 
BAI Hong-cheng College of Resources and Environment, Southwest University, Chongqing 400716, China
Chongqing Key Laboratory of Agricultural Resources and Environment, Chongqing 400716, China
China Key Laboratory of the Three Gorges Reservoir Region's Eco-Environment, Ministry of Education, Chongqing 400716, China 
 
LIU Gao-yun College of Resources and Environment, Southwest University, Chongqing 400716, China
Chongqing Key Laboratory of Agricultural Resources and Environment, Chongqing 400716, China
China Key Laboratory of the Three Gorges Reservoir Region's Eco-Environment, Ministry of Education, Chongqing 400716, China 
 
WEI Shi-qiang College of Resources and Environment, Southwest University, Chongqing 400716, China
Chongqing Key Laboratory of Agricultural Resources and Environment, Chongqing 400716, China
China Key Laboratory of the Three Gorges Reservoir Region's Eco-Environment, Ministry of Education, Chongqing 400716, China 
sqwei@swu.sdu.cn 
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Abstract:
      The widely distributed natural organic matter (NOM) in the environment has important influences on the environmental behavior of heavy metals in soils. In this study, bulk NOM was divided into four fractions according to their molecular weight (F0:bulk NOM as the control; F1:fraction with molecular weight <5000 Dalton; F2:5000~10 000 Dalton; F3:10 000~30 000 Dalton; and F4:>30 000 Dalton), and the effects of different NOM fractions on Cd adsorption and desorption in purple soil in relation to their structure and properties were studied using a batch experiment. The results showed that NOM and its fractions significantly enhanced the Cd adsorption ability of the soil. The Cd adsorption rates of the soil increased by 6.25% to 61.22%, while the desorption rates decreased by 16.22% to 56.52% with the addition of 0.1%, 0.2%, and 0.5% C of NOM or its fractions to the soil. The promoting effect increased with the increase in NOM addition. At the same addition amount (0.5% C) of NOM fractions, the amount of Cd adsorption for F1, F3, and F4 was significantly higher than that of the bulk NOM (F0), while F2 showedthe opposite effect; the amount of Cd adsorption with the addition of F1 was about 37.98% higher than that of F0, and the desorption rate was about 38.63% lower. F2 decreased the amount of Cd adsorption by 6.68% and increased the desorption rate by 18.02%. The contents of C and H increased in the NOM fractions with the increase in their molecular weight, while the O content decreased.Accordingly, the ratios of O/C and (N+O)/C in the NOM samples decreased, thereby showing a lower oxidation state and a weaker polarity for the fraction with higher molecular weight. However, no linear dependence existed between the molecular weight of the NOM fractions and their effects on soil Cd adsorption. F1, which was a low molecular weight fraction, promoted Cd adsorption by soil mainly by altering soil pH, while the effects of fractions with higher molecular weight were possibly also relevant to their structural complexity.